Knowledge of fireproof cables
1 Introduction Fire proof (Flame proof) wire and cable is a general term for wire and cable with fire resistance performance, usually divided into two types of flame-retardant wire and cable and fire-resistant wire and cable. Starting from fire safety and fire rescue, more and more requirements are placed on the fire performance of wires and cables, for example:
Flame retardancy-retards and delays the spread of flames along wires and cables so that the fire does not expand.
Fire resistance (Fire resistance)-can maintain a certain period of operation in the case of flame combustion, that is, to maintain the integrity of the circuit (Circuit integrity).
Free halogen-The materials that make up wires and cables are free of halogens, and the combustion products are less corrosive.
Low halogen-The materials that make up wire and cable may contain halogen, but the content is low.
Low smoke (low smoke)-less smoke and dust generated when the wires and cables burn, that is, higher light transmittance.
Low toxicity (low toxicity)-the gas toxicity of wire and cable materials when burning is low.
The research and development of flame-retardant and fire-resistant wire and cable in China began in 1982. After 5 years, in 1987, many cable manufacturers have put into production and recognized by users. In view of the confusing naming and model of combustion characteristics at that time, the author proposed to classify the fire-resistant wires and cables according to the combustion characteristics of the wire and cable corresponding to the combustion test method, and use the first letter of Chinese pinyin as the prefix of the corresponding ordinary wire and cable model . Among them, the flame retardant wire and cable type ZR and the fire-resistant wire and cable type NH have been used until now.
With many new developments made in the development and research of fireproof wires and cables, the original models are no longer sufficient. In addition, more and more manufacturers have put into production, and when formulating enterprise standards, the need for each type of related models has caused new confusion. The most prominent performance is that the burning characteristics of wire and cable are the same, but the name and model are different. The industry and users strongly demand to change this situation, hoping to unify the models. To this end, this article proposes a method of compiling fire-resistant wire and cable models for future reference in compiling corporate standards or industry standards.
2 Principles for the preparation of fire-resistant wire and cable models (1) A model corresponds to a combustion characteristic. There are corresponding test methods and specific indicators that can be evaluated, and the first letter of Chinese Pinyin is used to simplify it.
(2) The model number is added before the ordinary wire and cable model by the prefix method.
(3) The inherent combustion characteristics of ordinary wires and cables are not given separately. (4) There is room for supplementary development.
At present, there are some differences between China's standards and IEC international standards, because some standards, IEC issued after China's standards, according to the principle of equivalent use of international standards, this difference will be eliminated in the future.
3 Description of model and usage
3.1 About flame retardant (ZURAN)
According to IEC 332, flame retardant is divided into single and bundled. More than ten years ago, China's wire and cable were mainly halogen-containing products such as polyvinyl chloride and neoprene. Passing a single vertical burning test is a basic requirement in the product standard, so it is not necessary to give a single flame retardant model. Bundle C is the basic requirement for flame-retardant wire and cable, and Class B and A are flame-retardant requirements that users must specify. Therefore, it is popular to use the first letter of flame retardant (ZURAN) ZR as the model.
The situation is different now. Polyolefins such as polyethylene, polypropylene, ethylene propylene, and natural butylbenzene are flammable materials. When their flame retardant products can pass a single vertical combustion test, they must be given a model to match the original flammability characteristics. the difference. This model uses Z. Bundle combustion is classified as flame retardant A, flame retardant B, flame retardant C, and flame retardant D, so it is distinguished by ZA, ZB, ZC, ZD models. Among them, the flame retardant Class D is a new proposal of IEC, which is suitable for wire and cable with an outer diameter of 12mm and below. The total volume of non-metallic materials used in the sample is only 1/3 of Class C, or 0.5L / m. It is the same as Class C if the fire supply time is 20min and the scorch height is less than 2.5m. Because this proposal has yet to be voted through.
In addition, IEC 332-3 has a provision that when doing A-type tests, if the samples are arranged at intervals (in the case where a core conductor is greater than 35mm2) can not be arranged in front of the standard ladder, they can be arranged at the rear, and AF / R Said. Or use a wide ladder (0.8m wide) all in front of the ladder (indicated by AF), and use double blowtorch for fire. However, if a large-sized cable can be run down in front of a standard ladder, a single blowtorch is used for fire, which is still recorded as AF. In order to simplify the model, for this type of situation are recorded as ZA.
3.2 About fire resistance (NAIHUO)
According to the national standard GB 12666.6-90, fire resistance is divided into two grades, A and B. The fire supply temperature of Class A is 950 ℃ ～ 1000 ℃, and the fire supply temperature of Class B is 750 ℃ ​​～ 800 ℃. Earlier, the NH model was used to indicate fire-resistant wire and cable, which is equivalent to the Class B of China's standard according to the requirements of the IEC 331-1970 standard. Because some users require Class A refractory wire and cable, the model is expanded to NA and NB to show the difference. However, in the recently published standard IEC60331-1999 by the IEC, the fire supply temperature is still 750C to 800 ° C, and suggestions for increasing the test temperature are still under consideration. Therefore, if the new national standards are used in the same way, there is no distinction between Class A and Class B fire resistance. At that time, the model of refractory wire and cable can be simplified as the team. If the IEC classifies the test temperature in the future, our model has room for development.
It is worth noting that the UK has the most requirements for fire-resistant cables, so there are many models. Considering the impact of the United Kingdom on IEC, IEC has been considering increasing the test temperature, water spray and mechanical impact. Therefore, model C for additional impact (CHONGJI) and model S for additional water spray (PENSHUI) for future use .
Note: The fire resistance, water spray resistance and impact fire tests are carried out separately. For example, the cable type that passed the fire resistance at 950 ℃ 3h and 750 ℃ ​​is CY; the cable type that passed the 650 ℃ 3h fire resistance, 950 ℃ 20min fire resistance, 650 ℃ water spray and 650 ℃ impact requirements is ASWX, and so on. The highest level model is CwZ.
3.3 About Low Halogen (DILU), Halogen Free (WULU), Low Smoke (DIYAN), Low Capacity (DIDU)
Regarding low halogen (DILU), it is represented by D. The method of IEC60754-1: 1994 (GB / T 17650.1-1998 national standard) was used to determine the HCI content. There is no index in the standard, it is recommended that HCI ≤100 mg / g.
Regarding halogen-free (WULU), that is, low corrosivity, it is represented by W: IEC 60754-2: 1991 (revised in 1997), the national standard equivalently adopted in China is determined by the method of GB / T17650.2-1998, and the percussion standard is PH≥4.3, r (conductivity) ≤10ps / mm. Many countries or companies abroad set the halogen-free standard as HCI≤5mg / g, and the Chinese have followed suit, which is inappropriate. Because IEC 60754-1 has clearly stated that this method cannot be used to determine materials with an HCI content of less than 5 mg / g, that is, "halogen-free" cannot be determined. Secondly, when the HCI content is> 2 mg / g, the PH value of its aqueous solution is less than 4.3, which does not meet the requirements of IEC60754-2. In addition, some people think that the index set by the IEC is PH ≥ 4.3, while the index of Germany is PH ≥ 3.5, so the requirements of the IEC are higher than that of Germany. This is only a superficial phenomenon. In fact, the effect of the two is exactly the same. I have the opportunity to introduce another article.
Regarding low smoke (DIYAN), it is also indicated by D. Although it repeats with the low halogen D, it has been agreed, and it should not be misunderstood when the model is combined. The international standard for low smoke requires light transmittance ≥60%. It must be pointed out that the low-smoke of the wire and cable made by the so-called low-halogen and low-smoke materials based on PVC in China does not meet the above requirements, and low-smoke models should not be used. Unless otherwise stated in the product standard, such as the index for reducing the light transmittance, and indicating that the index is lower than the requirements of international standards or national standards, so as not to misunderstand users.
Regarding low toxicity (DIDU), D can no longer be expressed, but U. The relevant standard IEC is still under consideration. Currently used more is the British Navy Engineering Standard NES713, which is expressed by the toxicity index (TI). For example, the toxicity index of insulating materials is required to be less than 3, and the toxicity index of the sheath is less than 5. Some domestic manufacturers claim that they can provide halogen-free, low-smoke, and non-toxic cables. The non-toxic mentioned here is inappropriate and should be low-toxic. Because halogen-free and low-smoke materials burn, they produce toxic CO. If the materials contain P, N, and S, more toxic gases are generated.
3.4 About the combination of models
When a certain wire and cable has a variety of burning characteristics, according to international practice, a certain model and title are in the following order (no items should be omitted);
No (low) halogen-low smoke-low toxicity-flame retardant-fire resistant
E.g:
(1) Flame-retardant (A) type PVC insulated PVC sheathed power cable, model: ZA-VV
(2) Low halogen flame retardant (Class B) PVC insulated PVC sheathed power cable, model: DZB-VV
(3) Low halogen low smoke flame retardant (Class C) PVC insulated PVC sheathed power cable, model: DDZC-VV
(4) Halogen-free and low-smoke flame retardant (Class A) XLPE insulated steel tape pin-mounted polyolefin sheathed power cable, model: WDZA-YJY23 (number 3 for polyolefin sheath of outer sheath)
(5) Halogen-free low-smoke flame retardant (Class B) XLPE insulated polyolefin sheathed power cable, model: WDZB-YJY (polyolefin model Y does not use X, E, O or P, according to GB / T13849 ï¼1993)
(6) Halogen-free, low-smoke, fire-resistant (Class A) XLPE insulated polyolefin sheathed power cable, model: WDNA-YJY
(7) Fire-resistant (Class B) PVC insulated and PVC sheathed power cable, model: NB-VV
3.5 Problems that must be noted The method for determining the corresponding model and appellation based on the combustion characteristics of wires and cables is proposed above. The following are some of the current problems and how to deal with them as follows: (1) Do not wear high hats for flame retardant In order to achieve the flame retardant requirements of wire and cable, there are various methods. For example, the use of inorganic flame retardant-based cement filling (so-called "oxygen barrier", "fire barrier", etc.) or inorganic flame retardant-based paint coating flame retardant city (so-called " High flame retardant tape "," oxygen and fire barrier ", etc.), it plays a very important role in solving the flame retardant problem of cables composed of flammable materials such as cross-linked polyethylene insulation, and can even reach flame retardant class A s level. But don't wear it with "high flame retardant", "ultra high flame retardant", "ultra high flame retardant" hats, do not use GZR models. This is because, based on the same combustion test methods and indicators, they are all IEC 332-3 or GB 12666.5, so no matter what means and method is used to achieve flame retardancy, the model and title should be the same. The highest level of flame retardancy is currently ZA. It is worth noting that do not give fire-retardant cables new names, such as oxygen-barrier cables, fire-barrier cables, etc., otherwise, it will be difficult to understand in international bidding.
(2) Don't call it upside down. Your name is "halogen-free and low-smoke". His name is "low-smoke and halogen-free". There is no difference in substance, but the titles are not uniform. And the model can be WD or DW, and it is not unified upside down. In foreign countries, the titles are first halogen and then smoke. For example, the French Alcatel company called HALOGEN FREE LOW SMOKE CABLES (halogen-free low-smoke cable), the model is XLS; British Delta company called ZERO HALOGEN LOW SMOKECABLES To avoid self-made confusion), the model is OHLS, and so on. It can be seen that it is better to call it "halogen-free and low smoke". Similarly, "low smoke and low smoke" should not be called "low smoke and low smoke".
(3) Flame retardant should not be called flame retardant flame retardant. It is in line with internationally accepted FLAME RETARDANT, because RETARDANT is meant to delay and prevent. The Japanese call it flame retardant; and the flame retardant is called flame retardant. For unified appellation, good flame retardancy, Z is used instead of N.
(4) Do not use Pg fireproof cable for mineral insulated (MI) cables. Mineral insulated (MI) cables are different types of cables from organic insulated cables. Flame retardancy and fire resistance are one of its inherent characteristics. Therefore, in places where fire protection is required, MI cable can be recommended. But it is not necessary to call it fireproof cable again, so as not to be confused with organic insulated flame retardant cable and fire resistant cable. Do not add another model. The MI cable is called a fireproof cable in China. Some people think that its flame retardant and fire resistance performance is better. In fact, the test methods and assessment indicators are the same.
(5) Regarding the flame retardant rating of fire-resistant cables According to the newly published British Standards BS7629-1997 and BS6387-1994, the flame-retardant properties of fire-resistant cables are required to pass the single report vertical burning test. Therefore, if our country imitates it, the flame-retardant grade of the fire-resistant cable can be uniformly stipulated as a single flame-retardant when formulating the standard, and the flame-retardant code can be omitted in the model of the fire-resistant cable. Of course, if the user requests to increase the flame retardant level, then the flame retardant code can be inserted in the model.
The combustion characteristics of the cable are always aggregated, and the individual characteristics of each component are not taken into account, which not only makes the cable design useful, but also provides favorable conditions for the simplification of the model and appellation.
The above method of compiling fire-proof wire and cable model is based on the above, and conforms to the domestic custom Gucheng habit, simple and intuitive, easy to remember, and easy to add and delete features in the future. Hope to be accepted or put forward by everyone.
A rice cooker or rice steamer is an automated kitchen appliance designed to boil or steam rice. It consists of a heat source, a cooking bowl, and a thermostat. The thermostat measures the temperature of the cooking bowl and controls the heat. Complex rice cookers may have many more sensors and other components, and may be multipurpose. Cooking rice has traditionally required constant attention to ensure the rice was cooked properly, and not burnt. Electric rice cookers automate the process by mechanically or electronically controlling heat and timing, thus freeing up a heating element on the cooking range that had to be otherwise occupied for rice cooking. Although the rice cooker does not necessarily speed up the cooking process, with an electric rice cooker the cook's involvement in cooking rice is reduced to simply measuring the rice, preparing the rice properly and using the correct amount of water. Once the rice cooker is set to cook, the rice will be cooked with no further attention.
Features:
For modern home rice cookers, the smallest single-person model cooks 1 rice cup (180 ml), whereas large models can cook 10 cups. Commercial models can cook 20 or more cups. As a possible source of confusion, model specifications and names may list either cooked or uncooked capacity. Rice roughly doubles in size during cooking; therefore, a 10 cup (uncooked) rice cooker can produce up to 20 cups of cooked rice. The prices vary greatly, depending on the capacity, features, materials used, and the country of origin.
The majority of modern electric rice cookers are equipped with a stay-warm or keep-warm feature, which keeps the rice at an optimal temperature for serving without over-cooking it. Some gas cookers also have electric stay-warm mechanism. However, the usefulness of this feature degrades over time, a microwave may be more energy efficient or better suited to reheat rice that will sit longer than four hours.
Some rice cookers use induction heating, with one or more induction heaters directly warming the pot. This can improve energy efficiency.
Most modern rice cookers use aluminium for the inner cooking bowl. There are some models that use stainless steel instead of aluminium. Various other materials, such as copper, pure carbon, ceramic, and diamond powder coating, may be used for higher heat conductivity or better taste.
The pressure-cooking models can raise the water's boiling point higher, e.g., from 100 °C at 1.0 atm up to about 110 °C at 1.4 atm, which speeds cooking. The pressure-cooking models can also be used in high altitude areas, where the boiling temperature is below 100 Celsius. Pressure cookers are also suitable for cooking brown rice (which contains oils and bran fiber that cook differently from pure white rice starch). Some pressure rice cookers have a varying pressure control mechanism (named the "dual-pressure" method) that creates repeated pressure/release cycles during the cooking.
There also exist mechanisms to collect and return the boiled over liquid to the inner rice bowl.
Many cookers now have microprocessor-controlled cooking cycles, which are often used to adjust for rice and cooking type.
Applications
Rice cookers are typically used for the preparation of plain or lightly seasoned rice. Each rice cooker model may be optimized to cook a certain type of rice best. For example, most Japanese rice cookers are optimized for cooking Japanese rice and may not be the best for other types of rice[citation needed], although cooking time can be lengthened simply by more water.
The typical method of cooking long grain rice is boil-and-strain and/or steaming method. The absorption method used in Japanese rice cookers will produce slightly different texture and taste, usually stickier rice.
Brown rice generally needs longer cooking times than white rice, unless it is broken or flourblasted (which perforates the bran).
Different varieties of rice need different cooking times, depending on their grain size, grain shape, and grain composition. There are three main types of Asian rice: Oryza sativa subsp. indica, i.e., Indian rice (long grain rice, e.g., basmati rice and Thai jasmine rice), O. sativa subsp. javanica, i.e., Java rice (large grain rice) and O. sativa subsp. japonica, i.e., Japanese rice (medium grain rice, e.g., Calrose rice, short grain rice, e.g., most Japanese rice and risotto rice).
African rice, Oryza glaberrima, is an entirely separate species, but can be cooked in the same way. Zizania is not even in the same genus, although it is often called a rice (or "water oats"); it, too, can also be cooked in a rice cooker.
A rice cooker can be used to cook many boiled or steamed granular foods, such as pot barley, bulgar wheat, and dal. Provided the ingredients have similar cooking times, a rice cooker can cook mixtures such as khichdi. Some rice cookers can be used as automated couscoussiers, cooking couscous and a stew simultaneously.
Rice Cooker
Rice Cooker,Drum Rice Cooker,Deluxe Rice Cooker,Straight Rice Cooker
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